Electrodes for arc furnaces

ABSTRACT

Lateral arcing in arc furnace may be reduced by using an electrode having a bonded carbonaceous core containing a nitrogen-generating material.

United States Patent Sharp 1 Jan. 22, 1974 1 ELECTRODES FOR ARC FURNACES 2,336,095 10/1945 Edgar et a1. 252/511 2,767,289 10/1956 Robinson 1 252/510 [75] lnvenm" Dav"! Sharp Brmmgham 2,744,945 5/1956 Johnson 313/356 England 3,342,752 9/1967 Wade 252/511 Assig ee Foseco Inte ati nal ROblCtte Birmingham, England FOREIGN PATENTS OR APPLICATIONS [22] 1971 554,729 3/1958 Canada 252 510 [211 App]. No.1 136,188

Primary Examiner-.1. Travis Brown [30] Foreign Application Priority Data flags/ant Examiner-J. P. Brammer Apr. 21, 1970 Great Britain 19041/70 Attorney, Agent, or Firm-Wolfe, Hubbard, Leydig,

Voit & Osann [51] Int- Cl. [58] Field of Search... 252/510, 511; 313/354, 356, 1

313/357; 13/18 Lateral arcing in arc furnace may be reduced by using an electrode having a bonded carbonaceous core con- [56] References C'ted taining a nitrogen-generating material.

UNITED STATES PATENTS 5/1908 Price 252/510 2 Claims, N0 Drawings 1 ELECTRODES FOR ARC FURNACES This invention relates to electrodes for arc furnaces.

In the electric arc furnace, an arc is generally used to melt a charge of scrap metal or to melt a charge of metal containing ore and reducing agent, e.g. a metal oxide and crushed coke. The arc may be struck directly between two electrodes, but is more commonly struck between one or more electrodes and the charge. The latter is almost always the case for furnaces of tons capacity and over. The arcs used are generally of very high currents, usually greater than 30,000 Amps.

During the operation of such furnaces, and especially at the start of melting a charge of material, the arc is generally very unstable. This instability is due to a number of reasons, for example the irregular shape of the charge, and inhomogeneities in the furnace atmosphere. One of the undesirable results of this instability is a tendency for the arc to be deflected on to the side walls of the furnace. This is not only wasteful of the power consumed, but can lead to damage to the furnace itself. Additionally the consequent surges in the power consumption of the are are highly undesirable as placing a strain on the power supply and are control apparatus.

If the arc length could be shortened the tendency for the arc to flare on to the side walls would also be reduced and consequently less damage would be caused to the refractories which line the side walls. Such a situation will not assist arc stability and should only be used where furnace conditions are such that a consistent arc can be obtained under these conditions.

It has been found that by generating nitrogen in the arc the amount of flare to the walls is decreased and hence the refractory lining on the side walls of the furnace is preserved. The arcing is reduced and the incidence of deflection of the arc is minimised.

According to the present invention there is provided an arc furnace carbon electrode comprising an outer hollow cylinder consisting substantially of graphite, and an inner core, the said core containing a material which, in use of the electrode, generates gaseous nitrogen in the arc, and a proportion of carbonaceous carrying material and which is bonded together by a binding agent. Preferred binding agents are carbonaceous, such as tars, pitches and bitumens, but others may also be employed, for example cold-setting ureaformaldehyde, phenol-formaldehyde or furane resins. Epoxy resins may also be used as binder. Nitrogen containing resins are a preferred class of binder.

The nitrogen generating material may be selected from a wide variety of nitrogen-containing materials, both inorganic and organic. As inorganic materials, there may be noted various nitrates and nitrites, and various ammonium salts, hydroxylamine salts and hydrazine. Ammonium nitrate itself is not preferred due to its hazardous nature. Organic materials may be amines or amides, various nitroand nitrosocompounds, and urea and melamine formaldehyde resins. Three particular materials of value are sodium azide, sodamide and sodium nitrite. In addition, in certain conditions it is possible to use one material both as binder and as nitrogen generating material.

The following example will serve to illustrate the invention:

EXAMPLE Core mixtures were made up as follows (by weight):

Mixture l Mixture 2 Mixture 3 These mixtures were used as cores in furnace electrodes. In use, the arc formed using these electrodes showed little tendency to flare onto the side walls of the furnace, and was shorter and more stable.

I claim as my invention:

1. In an arc furnace carbon electrode comprising an outer hollow cylinder consisting essentially of graphite and an inner core for use in the melting of metal and in the production of metal from metal-containing ore and a reducing agent, in an arc furnace, the improvement that the inner core contains a material which, under the action of the arc in use of the electrode, generates gaseous nitrogen in the arc, and a proportion of carbonaceous carrying material and which is bonded together by a binding agent, said nitrogen generating material being selected from the group consisting of inorganic nitrites, ammonium salts, hydroxylamine, hydrazine, organic amines and amides, sodium azide, sodamide and sodium nitrite.

2. An electrode according to claim 1 wherein the binder is selected from the class consisting of tars,

pitches and bitumens. 

2. An electrode according to claim 1 wherein the binder is selected from the class consisting of tars, pitches and bitumens. 